This section outlines procedures to document the basic sedimentology of the deposits recovered during Leg 195, including lithologic classification, core description, smear slide description, color spectrophotometry, and X-ray diffraction.
The description of Leg 195 lithologies follows the ODP classification scheme (Mazullo et al., 1988). Composition of biogenic components and texture of siliciclastic particles are the definition criteria for sedimentary lithologies. Biogenic components consist of the skeletal remains of open-marine calcareous and siliceous microfauna and microflora derived from foraminifers, coccolithophorids (nannofossils), and radiolarians, as well as subordinate diatoms, sponge spicules, and silicoflagellates. Siliciclastic detrital components are composed of quartz, feldspar, heavy minerals, and clay minerals, as well as lithic rock fragments. Moreover, volcaniclastic components are intercalated in sediment sequences. At Site 1200, where we drilled into the summit of a mud volcano, serpentine deposits comprise the principal lithology. The principal name of a lithology refers to the component that exceeds 50% of the total composition.
The principal name of biogenic sediments and sedimentary rocks relates to the chemical composition, the major components, and the degree of compaction and induration. The following names are used: "ooze" for unconsolidated calcareous and/or siliceous biogenic sediments, "chalk" for friable biogenic sediment composed predominantly of calcareous biogenic grains, and "chert" for indurated biogenic sediment composed predominantly of siliceous biogenic grains.
The principal name of the biogenic sediment is preceded by major modifiers and followed by minor modifiers that may refer to mixed biogenic oozes and siliciclastic components. Sediments containing >50% siliciclastic material are classified separately (see "Siliciclastic Sediments"). Components in the range of 25%-50% modify the principal name (e.g., foraminifer ooze, nannofossil chalk, and radiolarian chert). In some cases, the identification and differentiation of individual components could be ambiguous, so we relate to more informal terms such as calcareous ooze or biosiliceous ooze. Components in the range of 10%-24% are added with the suffix "-bearing" (e.g., foraminifer-bearing nannofossil ooze). Components with abundances <10% are not named unless they are very important for interpretation (e.g., foraminifer-bearing radiolarian ooze with minor diatoms).
Biogenic sediments including between 25% and 50% siliciclastics are not referred to as oozes, chalks, or cherts. In this case, the principal name is followed by textural assignment of the major siliciclastic grain size (e.g., foraminifer silt or diatom-bearing nannofossil clay).
Siliciclastic sediments are composed of detrital mineral and rock fragments derived from plutonic, sedimentary, and metamorphic rocks. If the total siliciclastic component of the sediment is >50%, the principal name is determined by the relative proportions of sand, silt, and clay grain sizes when plotted on a Shepard (1954) classification diagram (Fig. F2). For siliciclastic sediments, the principal name describes the texture and is assigned according to the following guidelines:
Debris-flow facies encountered at Site 1200 (South Chamorro Seamount) are characterized by poorly sorted serpentine diamict facies. The term diamict is used as a nongenetic term for materials consisting of matrix-supported admixtures of clasts (defined here as fragments larger than sand size [2 mm]). It should be noted that existing ODP classifications do not adequately address nonsorted or poorly sorted admixtures of siliciclastic sediments, such as diamicts. The classification of poorly sorted sediments containing gravel is based on Moncrieff (1989) (Fig. F3). Clast-supported admixtures are named conglomerates when the clasts are rounded and breccia when the clasts are angular.
The following two classes of induration or lithification for siliciclastic sediments were adopted and modified from Leg 105 (Shipboard Scientific Party, 1987):
Although the sedimentary succession at Site 1201 in the Philippine Basin contains abundant detrital volcaniclastic material, the deposits are not referred to as primary volcaniclastic sediments because they were subsequently reworked and redeposited by turbidity currents. As a result, they have been classified as siliciclastic sediments (see "Siliciclastic Sediments").
Like volcaniclastic rocks, serpentine deposits represent lithologies that cannot clearly be related to one genetic mode. Although they originate from disaggregated metamorphosed ultramafic rocks, their emplacement via cold gravitational flows implies sedimentary processes. Here, we adopt the classification scheme of serpentine deposits developed by Leg 125 scientists (Shipboard Scientific Party, 1990). This classification includes the degree of compaction, mineralogical composition, and structural features. Serpentine deposits contain >50% serpentine-rich material in association with other primary or secondary authigenic minerals, such as aragonite, chlorite, epidote, and zoisite. Unconsolidated material is referred to as serpentine and indurated material as serpentinite, respectively. When serpentine is present in amounts <50% or is not associated with nonbiogenic aragonite >50%, the sediment and sedimentary rock classification scheme previously described is used.
The principal name of serpentine deposits is preceded by appropriate textural and compositional modifiers. The textural modifier is placed nearest the principal name and defines the dominant grain size (e.g. silt-sized serpentine or sand-sized serpentine). The compositional modifiers are listed in order of decreasing abundance to the left of the textural modifier and the principal name. Here, our classification differs slightly from that of Leg 125 so that our use of modifiers is consistent with nomenclature techniques used in previous sections of this chapter. A value of 25%-50% of a component qualifies for major compositional modifier status (e.g., chlorite sand-sized serpentine). A value of 10%-24% of a component qualifies for minor compositional modifier status and is hyphenated with the word "-bearing." (e.g., zoisite-bearing sand-sized serpentine). A value of <10% of an unusual important component (e.g., aragonite) qualifies for minor compositional modifier status (e.g., zoisite-bearing, chlorite silt-sized serpentine with minor aragonite).
Serpentinites are
frequently brecciated. If large clasts are set in a finer-grained serpentine
matrix, then the material is named serpentinite breccia (without tectonic or
sedimentary implications) with subsequent modifiers describing the matrix.
Sheared phacoidal serpentine is composed of scales or chips of serpentine 
1
mm in size, which may have slickensided surfaces and whose long axes define an
anastomosing foliation. This foliation may enclose angular to subangular blocks
of unsheared serpentinite (1
cm in size) or may be associated with horizontal or vertical convolute bedding.
Information from the macroscopic description of each core was recorded manually for each core section on visual core description forms (VCDs). This information was condensed and entered into AppleCORE (version 8.1b) software, which generates a simplified, one-page graphical description of each core ("barrel sheet"). Barrel sheets are presented with split-core photographs (see the "Core Descriptions" contents list). The lithologies of the recovered sediments are represented on barrel sheets by symbols in the column entitled "Graphic Lithology" (Fig. F4).
The color (hue and chroma) of the sediments was determined visually using the Munsell soil color charts (1975). A wide variety of features that characterize the sediment, such as bed thicknesses, primary sedimentary structures, bioturbation parameters, soft-sediment deformation, and structural and diagenetic features are indicated in columns to the right of the graphic log. The symbols are schematic but are placed as close as possible to their proper stratigraphic position. (For exact positions of sedimentary features, the detailed section-by-section paper core description forms produced on the ship can be obtained from ODP.)
Bed thickness is characterized by the terms "very thick bedded" (>100 cm thick), "thick bedded" (30-100 cm thick), "medium bedded" (10-30 cm thick), "thin bedded" (3-10 cm thick), and "very thin bedded" (1-3 cm thick) (McKee and Weir, 1953). Stratigraphic intervals <1 cm thick are characterized by the term "lamination."
Deformation and disturbance of sediment that resulted from the coring process are indicated by symbols in the "Drilling Disturbance" column (Fig. F4). Blank regions indicate the absence of coring disturbance. Detailed accounts of drilling disturbance appear in many previous ODP reports (e.g., Shipboard Scientific Party, 1995). Locations of samples taken for shipboard analysis are indicated in the "Samples" column.
A summary lithologic description with sedimentologic highlights is given in the "Remarks" column of the barrel sheet. This description provides information about the major sediment lithologies, important minor lithologies, an extended summary description of the sediments, including color, composition, sedimentary structures, trace fossils identified, extent of bioturbation, the age of the sediments as determined by shipboard paleontologists and paleomagnetists, and other notable characteristics. Descriptions and locations of thin, interbedded, or minor lithologies that could not be depicted in the "Graphic Lithology" column are presented in "Remarks," where space permits.
Lithologic characterization on the basis of visual core descriptions was verified by analyses of smear slides and thin sections, which provide crude estimates of grain-size distributions and the relative abundances of biogenic, siliciclastic, volcanic, and serpentine constituents. The visual estimates are based on area proportions and are qualitative in nature. Fine-grained particles such as clays and nannofossils are often underestimated. At Site 1201, the thin sections also provide insights into the diagenetic features of sandstones. The positions of smear slide and thin section samples taken from each core for shipboard analysis are indicated by "SS" and "TS" in the "Sample" column on the core description form.
Reflectance of visible light from the surface of cores was routinely measured downcore using a Minolta spectrophotometer (model CM-2002) mounted on the archive multisensor track (AMST). The AMST measures the archive half of each core section. The purpose of measuring the visible light spectra was to provide a continuous stratigraphic record of color variations downcore for visible wavelengths (400-700 nm). Spectrophotometer readings were taken when the core sections were wet and after the surface of each core section was cleaned. The measurements were then automatically taken and recorded by the AMST, which permits measurements at evenly spaced intervals along each core. Each measurement consists of 31 separate determinations of reflectance in 10-nm-wide spectral bands from 400 to 700 nm. Additional detailed information about the measurement and interpretation of spectral data with the Minolta spectrophotometer can be found in Balsam et al. (1997, 1998, 1999, 2000).
Relative abundances of the
main silicate and carbonate minerals were determined semiquantitatively on both
the bulk sediment fraction (Sites 1200 and 1201) and on the clay fraction (Site
1201) using a Philips model PW1729 X-ray diffractometer with CuK
radiation (Ni filter).
Each bulk sediment sample
was freeze-dried, crushed, and mounted with a random orientation in an aluminum
sample holder. Instrument conditions were as follows: 40 kV, 35 mA, goniometer
scan from 2° to 70°2
for bulk samples, step size = 0.01°2,
scan speed = 1.2°2/min,
and count time = 0.5 s. Peak intensities were converted to values appropriate
for a fixed slit width. An interactive software package (MacDiff 4.0.4 PPC) was
used on a Macintosh computer to identify the primary minerals (public domain
software is available on the World Wide Web from http://www.pangaea.de).
Diffractograms were peak-corrected to match the primary quartz peak at 3.343 Å.
In the absence of quartz, no peak correction was applied. Identifications are
based on multiple peak matches, using the mineral database provided with
MacDiff. Relative proportions of quartz, feldspar, carbonates, serpentine,
brucite, zeolites, carbonates, and clay minerals were estimated using peak
intensity ratios. Relative abundances reported in this volume are useful for
general characterization of the sediments but are not precise quantitative data.
Clay mineralogy was also
examined and verified by XRD on selected subsamples of the clay fraction (
2
µm). For grain-size separation, 3-g samples of bulk sediment were disaggregated
and washed with 25 mL of distilled water in 50-mL centrifuge tubes. Centrifuging
for 15 min at 1500 rounds per minute (rpm) removed salt from the samples. After
decanting the wash water, 25 mL of Calgon solution was added to the samples in
50-mL beakers. The samples were then placed in a sonic bath for up to 15 min to
suspend the clays by ultrasonic disaggregation and then centrifuged for 5 min at
1000 rpm to settle the >2-µm particles. The clays that remained in
suspension were collected from the top 1 cm of the solution with an eye dropper.
Two oriented clay mounts of each sample were made by placing drops of the clay
solution onto glass slides that were then dried at room temperature. One slide
was first analyzed in the air-dried state. Then it was solvated with ethylene
glycol for at least 12 hr and reanalyzed to determine the presence of expandable
clays. The second slide was analyzed after being heated to 550°C for 1 hr to
collapse kaolinite and smectite. All oriented clay mounts were scanned from 2°
to 35°2
in 0.010° increments.
